Sticky rubbers and plastomers, including heterophasic polymers comprising such, generally must be produced in solution phase polymerization processes utilizing a solvent at temperatures above 120° C., and typically above 135° C. This has been necessary to prevent reactor fouling. The reactor effluent in these processes is a liquid solution comprising the rubber or plastomer and a substantial amount of solvent. To obtain the final product, the solvent must be separated from the rubber or plastomer. To do this, the reactor effluent is typically heated under pressure in a separator to create a solvent-rich phase and a rubber- or plastomer-rich phase, and then both phases will need further separation by bifractionation. The process is time-consuming and not cost effective.
It would be more efficient and economical to polymerize rubbers and plastomers using a supported catalyst system in gas or slurry phase processes. Gas phase processes do not require substantial use of solvents or the corresponding sophisticated separation processes. In these processes, the reactor is typically a fluidized bed comprising monomer and comonomer primarily in the gas phase and fluidized solid particles comprising catalyst components and polymer. The reactor effluent comprises solid polymer granules, rather than a liquid solution of polymer in solvent. Slurry processes, on the other hand, still use substantial amounts of solvents but usually involve much simpler processes for separating solvent from the product than solution phase processes.
Both gas and slurry processes, however, have conventionally been limited in their ability to make rubbers, plastomers, or random copolymers (RCPs), as well as heterophasic polymers comprising such, without reactor fouling. Some semicrystalline rubbers can be produced in gas or slurry processes, but these processes require the addition of an anti-sticking agent such as carbon black to the reactor to reduce the possibility of fouling and assist in polymer handling. As such, the processes are extremely messy and often require dedicated equipment to prevent contamination. It would be advantageous to be able make rubbers and plastomers in gas or slurry phase without the requirement of anti-sticking agents.
Recently, efforts have also been made to prepare heterophasic polymers, such as an impact copolymer (ICP) having a stiff porous matrix phase and a sticky phase filling the pores of the matrix, using newly developed supported metallocene (MCN) catalysis technology to capitalize on the benefits such catalysts provide. Polymers prepared with such single-site catalysts often have narrow molecular weight and composition distributions, low extractables, and a variety of other favorable properties. Unfortunately, common MCN, immobilized on a conventional support coated with an activator such as methylalumoxane (MAO), has not been able to provide copolymer components with sufficiently high sticky phase (e.g., rubber) loadings under commercially relevant process conditions. The pore surface area of the stiff matrix phase derived from these conventionally supported catalyst systems is generally not high enough to fill a sufficient amount of sticky phase in the pores of the matrix. The formation of rubber or plastomer in a separate phase outside the matrix is undesirable because it can result in severe reactor fouling.
The structure of the support used in a catalyst system can affect the structure of the polymer produced. Highly porous supports, such as high surface area silicas, have been used in polymerization processes. However, such supports have not generally been used in sequential polymerization processes for making heterophasic polymers comprising sticky fill phases, likely because of the potential for such supports to reduce the mechanical strength of the matrix phase. A highly porous support (e.g., having high surface area) may generate a more porous polymer than a less porous support, other factors being equal. This is desirable for the matrix phase of an ICP because it can hold more fill phase polymer. However, the more porous polymer may have reduced pore wall thickness, resulting in a reduction in mechanical strength of the matrix phase that is not acceptable for most applications.
Background references on the use of high surface area silicas include WO 2004/092225, which discloses MCN polymerization catalysts supported on silica having a 10-50 μm particle size (PS), 200-800 m2/g surface area (SA), and 0.9 to 2.1 mL/g pore volume (PV), and shows an example of a 97 μm PS, 643 m2/g SA and 3.2 mL/g PV silica (p. 12, Table I, support E (MS3060)) used to obtain isotactic polypropylene (pp. 18-19, Tables V and VI, run 21).
EP 1 380 598 discloses certain MCN catalysts supported on silica having a 2-12 μm PS, 600-850 m2/g SA, and 0.1 to 0.8 mL/g PV, and shows an example of silica having a 6.9 μm PS, 779 m2/g SA and 0.23 mL/g PV (p. 25, Table 3, Ex. 16) to obtain polyethylene.
EP 1 541 598 discloses certain MCN catalysts supported on silica having a 2 to 20 μm PS, 350-850 m2/g SA, and 0.1 to 0.8 mL/g PV (p. 4, lines 15-35), and shows an example of a 10.5 μm PS, 648 m2/g SA and 0.51 mL/g PV silica (see p. 17, Example 12) for an ethylene polymerization.
EP 1 205 493 describes a 1126 m2/g SA and 0.8 cc/g structural porous volume (small pores only) silica support used with an MCN catalyst for ethylene copolymerization (Examples 1, 6, and 7).
JP 2003073414 describes a 1 to 200 μm PS, 500 m2/g or more SA, and 0.2 to 4.0 mL/g PV silica, but shows examples of propylene polymerization with certain MCNs where the silica has a PS of 12 μm and 20 μm.
JP 2012214709 describes 1.0 to 4.0 μm PS, 260 to 1000 m2/g SA, and 0.5 to 1.4 mL/g PV silica used to polymerize propylene.
Other references of interest include US 2011/0034649; US 2011/0081817; Madri Smit et al., Journal of Polymer Science: Part A: Polymer Chemistry, Vol. 43, pp. 2734-2748 (2005); and “Microspherical Silica Supports with High Pore Volume for Metallocene Catalysts,” Ron Shinamoto and Thomas J. Pullukat, presented at “Metallocenes Europe '97 Dusseldorf, Germany, Apr. 8-9, 1997.
None of the references discussed disclose use of a high surface area support in a sequential polymerization process to produce a heterophasic polymer comprising a stiff porous matrix phase and a sticky fill phase. There is need for new catalyst systems and processes that enable such polymers to be produced in gas and slurry phase polymerization processes without the use of substantial amounts of solvents and/or anti-sticking agents. There is a need for processes that take advantage of the favorable properties that a highly porous support and MCN catalysis technology can provide to produce materials that meet the needs of particular applications, such as providing one or more of: improved economics by making sticky polymers in low cost in use processes, improved toughness or other properties, low extractables, bimodal MWD, bimodal composition distribution, bimodal particle size distribution (PSD), a high fill loading of a fill phase polymer in a matrix phase polymer, and combinations thereof. There is a need for gas and slurry phase processes that enable the preparation of bimodal compositions comprising one or more of ethylene- and propylene-based rubbers, RCPs, and ethylene-based plastomers using a single catalyst system.